1. Field of the Invention
The present invention relates to a process for producing an infusible and insoluble granular sulfurized material by reacting a petroleum heavy material and sulfur with stirring in the presence of a reaction medium and further in the presence of, if necessary, an infusible and insoluble solid material. Furthermore, the invention relates to a process for producing granular carbon comprising carbonizing the above described granular sulfurized material and further to a process of producing granular activated carbon comprising and activating the above described granular sulfurized material. 2. Description of the Prior Art
An infusible and insoluble sulfurized material obtained by reacting a heavy hydrocarbon material, such as asphalt and pitch, and sulfur is useful for purposes such as various fillers, reinforcing agents, oil absorbents, and metal collectors and further the sulfurized material has quite excellent properties as an intermediate in the synthesis and manufacture of carbon disulfide, carbon articles, ion exchangers, adsorbents, etc., and further can be expected to have various applications. Therefore, processes for producing such a sulfurized material have been investigated for a long time and some are described in, for example, the specifications of U.S. Pat. Nos. 2,447,004; 2,525,343; 2,539,137; 2,585,454; and 3,248,303 and French Pat. No. 1,479,451. In these known processes, infusible sulfurized materials are produced by adding sulfur to a heavy hydrocarbon such as asphalt, etc., and reacting them by heating. However, in these processes an important disadvantage occurs in that bubbles of hydrogen sulfide generated by the reaction with the sulfur are incorporated in the reaction product to a great extent. That is, when a hydrocarbon such as asphalt is reacted with sulfur, the viscosity of the reaction product increases remarkably as the reaction progresses and the product becomes an infusible and insoluble sulfurized material passing through a rubbery or viscous state. In this reaction course, the bubbles of hydrogen sulfide formed in the reaction are easily broken and released from the reaction system in the early stage of the reaction when the viscosity of the reaction system is comparatively low but as the reaction progresses the viscosity of the reaction system increases making the release of the bubbles difficult and finally only a spongy sulfurized material having a low bulk density and mechanical strength is obtained. Such a disadvantage can be improved to some extent by controlling the rate of temperature rise so that the reaction proceeds slowly but in this case there is the difficulty that a long period of time is required to finish the reaction, which reduces the efficiency greatly.
A second problem is that the infusible sulfurized product agglomerates in the reaction vessel to form lumps. The withdrawal of the lumpy material and granulating the material by crushing or by grinding and molding the lumpy material is quite inefficient and requires a troublesome step, which makes the production process uneconomical. In U.S. Pat. Nos. 2,447,005 and 2,447,006 processes are described to minimize the above described disadvantage by spraying a uniform liquid mixture of a heavy hydrocarbon and sulfur into a heated reaction zone to cause their reaction under heating but these processes are unsuitable from a practical standpoint since they require a complicated apparatus and specific techniques.
A third problem is that the reaction temperature for obtaining the infusible sulfurized material is quite high. U.S. Pat. No. 3,248,303 teaches that it is necessary to heat the reaction system to temperatures higher than 450.degree. C to obtain the infusible product but when the reaction system is heated to such a high temperature, carbonization of the sulfurized material occurs inevitably. The carbonized material may be a useful material as various carbon materials and such is one of the important uses of the product but since the product has other uses than as such a carbonized material, the occurence of carbonization by the high-temperature heating restricts the uses of the sulfurized product.
As described above conventional processes of producing sulfurized materials are accompanied by various difficulties in the properties of the products and the processes themselves and hence development of a new process of producing the sulfurized material unaccompanied by such difficulties has been demanded.
Carbon articles are widely used in various industrial fields such as the general chemical industry, the electrochemical industry, the electric communication industry, the atomic energy industry, etc., as electrically conductive materials, refractory materials, chemically resistant materials, structural materials, lubricants, parts of machinery, etc. These carbon articles are prepared generally by grinding a carbonaceous material, kneading it with a binder such as pitch, a synthetic resin, etc., and molding the mixture into a form meeting the desired purpose. Natural graphite, anthracite, coal, coke, and charcoal have been mainly used as the carbonaceous material for producing the above described carbon articles but it is not always easy to secure a stable supply of these raw materials having high quality.
Therefore, petroleum raw materials which can be supplied in large amounts at a low cost have been evaluated and the petroleum coke industry using these raw materials has become an important industry. A process of producing petroleum coke is generally classified into a delayed coking process as described in Hydrocarbon Processing, 49 (9) 180 (1970). However, the powdery coke obtained by the fluid coking process does not provide high-grade carbon articles and thus is mostly used for fuel. On the other hand, the coke produced by the delayed coking process is quite useful for producing various carbon articles but the process is accompanied by such large disadvantages in that the crushing of the lumpy coke accumulated in a coking drum and withdrawing the coke from the drum is quite difficult, in that the process is unsuitable for continuous running, mechanization, and automation, and in that the running efficiency of the apparatus is quite low. Further the carbonization efficiency is not always satisfactory.
Therefore, a new process of producing carbon materials without the need for handling the lumpy materials which reduces the working efficiency and without forming powdery carbon which has a limited use has been desired. One process which attempts to meet these requirements, is a process in which fusible moldings such as pitch, etc., are converted into infusible moldings by subjecting the moldings to a chemical treatment or a heat treatment in an oxidizng atmosphere and then the infusible materials are subjected to a carbonization treatment. The conversion to an infusible state is attained by treating the fusible material with an oxidizing gas containing NO.sub.2, O.sub.2, O.sub.3, SO.sub.3, Cl.sub.2, Br.sub.2, air, etc., or an oxidizing liquid such as sulfuric acid, phosphoric acid, nitric acid, an aqueous solution of chromic acid, an aqueous solution of potassium permanganate, etc., at a temperature lower than the softening point of the fusible material as disclosed in Japanese Pat. Application OLS No. 31195/1973. However, such a process is accompanied by corrosion of the apparatus due to the use of the oxidizing material or is accompanied by the disadvantage that a long period of time is required for conversion to the desired infusible material.
Thus, from the aforesaid standpoint of difficulties in conventional processes for producing carbon materials, the development of a new process for producing granular carbon has been desired which can be practiced using a raw material available in a large amount at low cost without forming powdery carbon having limited use and further without the necessity for a specific operation for granulating the fusible material.
Furthermore, activated carbon is a most important material as an industrial adsorbent and is used in a large number of fields including not only as adsorbents in the food industry and the chemical industry but also as adsorbents for domestic refrigerators and water purifiers. Also, it has recently become clear that activated carbon is quite effective for the prevention and removal of environmental pollution such as air pollution and water pollution and from this standpoint the development of a technique capable of supplying a large amount of activated carbon having good quality at a low cost has been desired. Hitherto, activated carbon has been produced using wood or coconut shells as the main raw material but a stable supply of a large amount of activated carbon can not be expected from these raw materials. Recently, activated carbon has been produced using coal as the raw material but the type of coal which can provide activated carbon having good quality is obtained from a limited area and thus this technique also involves a large problem in supplying a large amount of good raw materials in a secure and stable manner.
From these points of view, recently attempts have been made to produce activated carbon from a raw material such as a petroleum heavy hydrocarbon which can be supplied in a large amount at a low cost. For example, a process wherein an alkali metal compound such as potassium sulfide, sodium hydroxide, sodium carbonate, and potassium thiocyanate is added to asphalt or pitch followed by carbonization and the carbonized material is activated and a process wherein a reaction product of asphalt or pitch with sulfuric acid or sulfur is carbonized and activated are known. However, in the process in which an alkali metal compound is added, the alkali metal compound must be removed by washing in a subsequent step and thus the process is not practical. Also, in the process in which sulfuric acid or sulfur is used, sulfuric acid or sulfur does not remain in the activated carbon and thus the step of removing such additive is unnecessary. However, in the process in which sulfuric acid is used, the treatment of sulfuric acid is dangerous since the sulfuric acid is present in a large amount and further the corrosion of the apparatus is a problem. On the other hand, in the process in which sulfur is used, although hydrogen sulfide may be formed during the production step, the corrosion of the apparatus is not a particular problem and hydrogen sulfide can be easily regenerated into sulfur by a Clauss reaction or a catalytic decomposition. Thus, the sulfur formed can be repeatedly used, which makes the process economically profitable. The active carbon obtained by the process in which sulfur is used has excellent properties the same as or superior to those of the active carbon obtained from coconut charcoal and the yield of the active carbon is high. In this case, however, unfortunately the sulfurized material is obtained as a sponge-like lumpy product and also the production of the sulfurized material in the form of discrete granules of a desired size having a sufficiently high mechanical strength is difficult as described above.
Also, the process of producing the aforesaid granular carbonaceous solid material is generally classified into a process comprising crushing a lumpy product and a process comprising molding or agglomerating a powdery product into a granular product using a suitable binder. In the former process, it is impossible to produce selectively a granular carbonaceous material having a definite grain size and the yield of grains having a desired grain size is low. Also, the activated carbonaceous material obtained by crushing has the disadvantages that it tends to be damaged during handling due to its irregular and angular form with fine pieces or powders being formed. On the other hand, a granular material obtained by molding is produced generally by mixing a powder of the base material and a binder, molding the mixture into granules, and then subjecting them to a heat treatment. Therefore, due to powder handling, the process has the disadvantages that the working efficiency is low, and as the binding strength between the binder and the grains of powder is weak, the grains in the formed material tend to be reduced to powder by friction. Also, with the molding process it is quite difficult to obtain a fine granular material having a grain size of from a few microns to about 1 mm.
In addition to the above-described processes, a process for producing granular carbon and granular activated carbon in which highly viscous pitch having a high softening point is molded into granules and then the granules are converted into an infusible state is known. However, in this case, although excellent granular carbon having high mechanical strength as compared with conventional products can be obtained since a binder is not used, extremely precise techniques are required for converting a fusible material such as pitch to an infusible state without deforming the material and in particular it is quite difficult to obtain a granular active carbon having grains larger than about 1 mm.